Looking Up: Seeing double among the stars

Peter Becker More Content Now

Friday

Sep 14, 2018 at 10:54 AMSep 14, 2018 at 2:32 PM

There’s a beautiful double star visible at the foot of the Northern Cross, easily seen in a small telescope the next clear September evening. Instead of one star, you will see two, one blue and there other gold.

Its name is Albireo, more technically called Beta Cygni. Albireo is one of the most popular binary, or double stars because it is so colorful and accessible. There are hundreds within reach of a small telescope, and even binoculars. Some are even triple stars.

To find Albireo, first find the Northern Cross, which is really a portion of the constellation Cygnus the Swan. Between 8 p.m. and 10 p.m., daylight savings time, stand due south and if you are in the mid-northern latitudes such as I am in Pennsylvania, look very high up.

Cygnus is reaching the zenith, the point in the sky straight overhead. The brightest stars easily form a pattern of a large cross, with the top star, Deneb, being the most brilliant. The star at the bottom end of the cross is Albireo.

To the left of Cygnus is the 0-magnitude star Vega, one of the brightest in the night sky. Vega is the brightest star of the constellation Lyra the Harp. Scanning down (south) from Albireo is the bright star Altair, the brightest star in Aquilia the Eagle.

These three bright stars, Deneb, Vega and Altair, form a large triangle informally known as the “Summer Triangle” which is not an official constellation.

Albireo, the double star, is very near the center of this triangle.

This star system is around 415 light years from the Sun. That’s how many years the light from Albeiro takes to reach our eyes. With eyes alone, the star appears to be single.

You can see Albeiro as double with large binoculars but you will need to be hold them rock steady — a tripod is much better — or lean them against something solid. A telescope of any size, magnifying at least 30x is preferred.

The brightest component (“Albireo A”) is gold in color and magnitude +3.1. Its companion (“Albireo B”) appears blue-green and is magnitude +5.1. Astronomers are not clear if these two stars are physically related, in that they orbit around a common point, or if this is an “optical double,” two stars that appear to be together by chance alignment.

Astronomers have discovered that Albiero A is actually a binary, thus making at least three stars in this stellar system.

The color contrast is striking and makes Albireo one of the favorite stars of summer and fall evenings.

There are many other fine double stars within easy reach. The Big Dipper is low in the northwestern sky on September evenings. Be sure to check the middle star in the “handle.” Known as Mizar, it is considered a good vision test if you can detect the fainter star, Alcor, right next to it without optical aid. A small telescope quickly shows Mizar and Alcor separated wide apart and Mizar split into a close double star. There is also a dimmer star easily seen in the same low-power eyepiece field, making a triangle with Mizar and Alcor.

A few other gorgeous double stars needing a small telescope and about 50x are Polaris the North Star; Gamma Andromedae and Eta Cassiopeiae.

Nu Draconis is such a wide pair they require only a pair of 7x binoculars. This double star is of one of the four making up the “head” of the constellation Draco the Dragon in the northern sky. On a September evening face south and look nearly straight up for the bright star Vega. Spin yourself around and facing north, trace a line down from Vega to a quadrangle of stars making up Draco’s “head.” Starting at the brightest of the four (Eltanin), on the very opposite corner is Nu Draconis.

There are hundreds more double stars which are easily split; others are so close they are a challenge. Good seeing — steady air — is important, as well as a well-aligned telescope.

Some double stars are of equal brightness, making them look like a pair of headlights coming right at you, or glowing cat eyes.One good source for those wishing to know more about observing double stars is the Astronomical League. Visit www.astroleague.org.

First quarter Moon is on Sept. 16.

Keep looking up. — Peter Becker is Managing Editor at The News Eagle in Hawley, PA. Notes are welcome at news@neagle.com. Please mention in what newspaper or web site you read this column.

Never miss a story

Choose the plan that's right for you.
Digital access or digital and print delivery.